`A = 1 + 2 + 3 + ............. + 1000`
`A = 1000 + 999 + 998 + ................ + 1`
`2A= 1001 + 1001 + 1001 + .............+ 1001`
`2A = 1001 . 1000`
`⇒ A = 1001 . 1000 : 2 = 500500`
`B = 1 + 3 + 7 + ....................... + 1001`
`B = 1001 + 999 + 997 + .........................+ 1`
`2B=1002 + 1002 + 1002 + .....................+1002`
`2B= 1002 . 1001`
`⇒ B = 1002 . 1001 : 2 = 501501`
`text(Vì A = 500500 và B = 501501)`
`text(Nên A < B)`
